Gametogenesis and Human Reproductive Biology: Oogenesis, Spermatogenesis, and Fertilization

Gametogenesis

The formation of gametes or sex cells.

Sperm (M)

Male gamete.

Egg (F)

Female gamete.

Gonads

Organs where gametes are produced; testes in males and ovaries in females.

Oogenesis (F)

The process of egg formation.

Spermatogenesis (M)

The process of sperm formation.

Meiosis

Involves two chromosomal reductions to produce four unique haploid daughter cells.

Ploidy

The number of sets of chromosomes in a cell.

Haploid

A cell with one set of chromosomes (1N).

Diploid

A cell with two sets of chromosomes (2N).

Testosterone

Male sex hormone.

Primordial Germ Cell (PGC)

Precursor to sperm/egg.

Spermatogonium

Male stem cell that undergoes spermatogenesis to become spermatozoa.

Sertoli Cells

Epithelial supporting cells of seminiferous tubules that provide nutrients.

Spermatid

Haploid gametid that develops into spermatozoa.

Leydig Cells

Cells that produce testosterone and have clear cytoplasm due to cholesterol.

Progesterone

Hormone released by corpus luteum to prepare the uterus for pregnancy.

Estrogen

Female steroid hormone produced in ovaries.

Follicle

Aggregation of cells with a single oocyte.

Primary Follicle

Immature follicle surrounded by one layer of granulosa cells.

Secondary Follicle

Maturing follicle with two theca and the antrum (fluid filled space).

Graafian Follicle

Follicle after meiosis 1 but before ovulation; contains a 2N oocyte and a large antrum.

Atretic Follicle

Degenerating follicle due to menstruation.

Zona Pellucida

Thin glycoprotein band separating oocyte from follicular cells.

Cortical Reaction

Triggered when a sperm breaks through the vitelline membrane, causing a chain reaction that hardens the egg membrane.

Zygote

The cell formed by the fusion of two nuclei during fertilization.

Gametogenesis

The formation of gametes or sex cells occurring within gonads (ovaries or testes) involving two chromosomal reduction divisions (meiosis) that result in haploid gametes.

Nuclear Fusion

The process that occurs during fertilization, where the haploid pronuclei of eggs and sperm combine, restoring the chromosomal complement to diploid status.

Oogenesis

The process of gametogenesis that occurs within the ovaries of a female, beginning with a primordial germ cell that produces an oogonium.

Primordial Germ Cell

A cell present since early development of the female that undergoes maturation to produce an oogonium.

Oogonium

A pre-reduction mitotic division cell that is diploid and produced from a primordial germ cell; typically, one is produced each month in humans.

Primary Oocyte

A diploid cell produced by mitosis from an oogonium, which will begin meiosis.

Yolk Platelets

Substances produced in the female's liver and carried to the ovaries that accumulate in the cytoplasm of the oocyte during its growth phase.

Follicle Cells

Cells that surround the oocyte, functioning in passing products such as yolk into the oocyte's cytoplasm and increasing in number as the oocyte grows.

Primary Follicle

An oocyte that is surrounded by follicle cells.

Antrum

A cavity formed by fluid accumulation around the oocyte, containing ovarian-produced hormones.

Estradiol

An ovarian-produced hormone that contributes to the fluid in the antrum and is fed back into the circulatory system of the female.

Secondary Follicle

A stage formed when undercutting occurs between the primary oocyte and surrounding follicle cells, creating an antrum.

Cumulus Oophorus

The basal 'stem' that attaches the primary oocyte to the follicle cells lining the antrum.

Corona Radiata

The series of follicle cells that wrap around the oocyte.

Stratum Granulosum

The collective name for follicle cells lining the antrum.

Tertiary Follicle

The stage marking the final maturation of a primary oocyte, characterized by a greatly enlarged follicle.

Progesterone

Another hormone present in the fluid of the antrum by the time of tertiary follicle formation.

Ovulation

The process when the primary oocyte bursts out of its tertiary follicle, completing meiotic division MI and entering the oviduct.

Secondary oocyte

The cell that reaches metaphase MII during its travel into the ostium and is mistakenly called an egg.

Ostium

The upper funnel-shaped opening into the oviduct where the secondary oocyte travels.

Polar Body I

The first polar body ejected during the meiotic division of the primary oocyte.

Polar Body II

The second polar body that gets ejected before nuclear fusion, allowing the secondary oocyte to become an egg.

Fertilization

The process required to drive the secondary oocyte to completion of MII, resulting in a true egg.

Zygote

The diploid condition that marks the beginning of an embryo after fertilization.

Corpus luteum

A hormone-secreting structure formed from the ruptured follicle that remains throughout the period of pregnancy.

Corpus albicans

A small, temporary structure that forms when a corpus luteum degenerates if pregnancy does not occur.

Spermatogenesis

The process of sperm production that differs from oogenesis and can produce millions of sperm.

Spermatogonium

A cell capable of producing a single primary spermatocyte through mitosis.

Primary spermatocyte

A diploid cell that results from a spermatogonium and quickly completes meiotic division MI.

Secondary spermatocyte

The haploid cells produced from the meiotic division of primary spermatocytes.

Spermatid

The haploid cells that result from the meiotic division of secondary spermatocytes.

Metamorphosis of spermatids

The process in which spermatids undergo changes to form mature sperm, including ejection of cytoplasmic fluid and formation of a tail.

Seminiferous tubules

Structures in the testes where spermatogonia are located and sperm production occurs.

Testicular tissue

The tissue in the testes that contains seminiferous tubules and various stages of sperm development.

Meiotic division MI

The first meiotic division that results in the formation of secondary oocytes or secondary spermatocytes.

Meiotic division MII

The second meiotic division that completes the formation of haploid cells from secondary oocytes or spermatocytes.

Interstitial cells

Cells that produce testosterone.

Spermatogonia

Cells that produce primary spermatocytes (2n).

Primary spermatocytes

Cells that produce secondary spermatocytes.

Secondary spermatocytes

Cells that produce spermatids.

Spermatids

Cells that transform into sperm.

Sertoli cells

Sustantacular tissue for sperm.

Oogonia

Cells that develop into primary oocytes.

Theca interna

Cells that produce estrogen.

Graafian follicle

Mammalian primary oocyte with antrum filled with liquor folliculi.

Egg

Forms with fertilization, releasing 2nd polar body before nuclear fusion.

Blastodisc

Living, dividing portion (embryo) on yolk of an egg.

Cortical reaction

Process triggered by sperm breaking through the oocyte, hardening the egg membrane.

Polyspermy

Fertilization of an egg by multiple sperm, prevented by the cortical reaction.